$ { {3} \times \left[\begin{array}{r}{4} \\ {0} \\ {-1}\end{array}\right] = {?} } $
To multiply a matrix by a number, multiply each item of the matrix by the number. ${\left[\begin{array}{r}{3}\times{4} \\ {3}\times{0} \\ {3}\times{-1}\end{array}\right]}$ Now, simplify: ${\left[\begin{array}{r}{12} \\ {0} \\ {-3}\end{array}\right]}$